Spot the Violation

FramingFloor framingLevel 32018 IRC

Sill plates on a new foundation

Looking down from the backfill at a corner of a new poured-concrete basement foundation before the floor framing goes on. Pressure-treated 2x6 sill plates sit on blue foam sill sealer along the top of the walls, held down with anchor bolts, round washers and hex nuts. Along the near wall the plate is three pieces butted end to end: a long piece running off the left edge of the frame with a bolt near its end, a short middle piece about 32 inches long with one bolt near its middle, and a corner piece with a bolt near each end. The return wall has its own plate and bolts. A tape measure lies on the short middle piece, hooked at its left end, with the bolt beside the 16 mark. The excavation and gravel basement floor show beyond the wall, and backfill soil is against the outside face. 246810121416182022
New basement foundation with sill plates bolted down

What's wrong here?

  1. The short middle plate section has only one anchor bolt, more than 12 in. from both of its ends
  2. Anchor bolts may be no more than 4 ft apart
  3. Each bolt must sit exactly on the centerline of the plate
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

The short middle sill-plate section, about 32 in. long, is held by a single anchor bolt 16 in. from each end. R403.1.6 requires at least two bolts in every plate section, with one within 12 in. of each end.

Correct choice: 1. The short middle plate section has only one anchor bolt, more than 12 in. from both of its ends

Each piece of sill plate has to be anchored on its own, because the bolts in the neighboring pieces do nothing to keep this one from lifting, rotating or sliding. R403.1.6 requires 1/2 in. anchor bolts at no more than 6 ft on center, at least two bolts per plate section, and a bolt within 12 in. of each end of every section (but no closer than seven bolt diameters, 3-1/2 in. for a 1/2 in. bolt). Its only one-bolt allowance is for walls 24 in. long or shorter that connect offset braced wall panels, which a sill-plate filler piece is not. Short filler pieces are where this rule gets missed: the bolts were set in the wet concrete for one plate layout, and the plate was cut differently later. The long piece and the corner piece here are fine, with bolts 8 to 10 in. from their ends and well under 6 ft apart.

How to fix it

Add anchors so the short piece has one within 12 in. of each end (and no closer than 3-1/2 in.), using approved anchors that give anchorage equivalent to a 1/2 in. bolt, such as epoxy-set threaded rod with 7 in. embedment or a listed retrofit anchor. Another option is to recut the plates so every section picks up two existing bolts placed correctly.

Code reference

  • IRC 2018 R403.1.6 — Foundation anchorage

    Wood sill plates must be anchored to the foundation with at least 1/2 in. steel bolts (or approved anchors) spaced no more than 6 ft on center and embedded at least 7 in. Bolts go in the middle third of the plate width with a nut and washer tightened on each. Each plate section needs at least two bolts, with one bolt no more than 12 in. and no less than seven bolt diameters from each end of the section.

    Drills citing R403.1.6

2024 IRC:same rule and number. Summaries of the 2024 IRC keep the 6 ft spacing, 7 in. embedment, middle-third placement and two bolts per plate section with one within 12 in. of each end. One secondary source says the 2024 edition also requires plate washers (per R602.11.1) on anchor bolts along required braced wall lines, with cut washers allowed elsewhere. If that applies statewide, the round cut washers shown here could matter under the 2024 code. Not confirmed against the printed 2024 IRC or a 2024-based Minnesota amendment. Confidence: low

Minnesota

MN status unverifiedConfidence: medium

Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). Minn. Rules 1309.0403 is reported to amend IRC R403.1.6: search-result excerpts say the Minnesota text keeps the 6 ft spacing and the two-bolts-per-section, 12 in.-from-each-end rule tested here, and adds an exception for foundation anchor straps spaced to give anchorage equivalent to 1/2 in. bolts. The Minnesota text could not be read to confirm this. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.

About the Minnesota Residential Code

Why the other choices are wrong

  • Anchor bolts may be no more than 4 ft apart. R403.1.6 allows anchor bolts up to 6 ft on center. Tighter spacing comes from the high-seismic anchorage provisions, which do not apply to typical Minnesota houses.
  • Each bolt must sit exactly on the centerline of the plate. R403.1.6 only requires bolts to be in the middle third of the plate's width, and these are.
  • Nothing. This installation is compliant. Every plate section needs at least two bolts, with one within 12 in. of each end (R403.1.6). The 32 in. filler piece has one bolt, 16 in. from each end.
Safety hazardLevel 3 · Master#anchor bolt#sill plate#foundation#plate section#new construction

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